The present invention relates to glass compositions for use as materials capable of intercepting ultraviolet radiation.
The percentages (%) appearing herein are all by weight unless otherwise specified.
Colored glass has been used as a material capable of absorbing light beams in ultraviolet or visible region, e.g., as a material for sharp cut glass filters on cameras. Such colored glass is produced by doping a glass material with microcrystals of semiconductor compounds which pertain to II-VI groups such as CdS, CdSe, CdSSe and the like. The microcrystals of semiconductor can intercept ultraviolet radiation by absorbing light beams at a specific wavelength passing through colored glass.
However, the foregoing cadmium compounds are toxic and cause health hazards to operators carrying out a producing process including preparation of a batch, transport, melting, etc. Moreover, it is difficult to dispose of the Cd compounds in the effluents and waste resulting from cutting, grinding, polishing and other processing, and consequently pollution problems are likely to occur. To avoid pollution, the contents of Cd and like compounds in waste water, are limited, for example, to 0.1 mg/l under the Water Pollution Control Law in Japan. For the above reasons, the production of colored glass requires a number of installations including equipment for treatment to control pollution, equipment for the disposal of sludge, etc. and therefore the Cd compound-doped glass is not an industrially suitable material.
The glass materials doped with microcrystals of CdS, CdSe, CdSSe or like compounds show a gradual inclination in a graph (.DELTA..lambda.) according to JIS B 7113 indicating the light transmittance plotted as ordinate and the wavelength plotted as abscissa (see, for example, FIGS. 2-4 attached hereto) and can not achieve a high absorption of light.
Multilayer-coated glass is used for similar applications. This type of glass is produced by vapor deposition of multilayer film on a glass product incapable of absorbing light beams in ultraviolet or visible region and is intended to intercept light beams in a specific wavelength range by utilizing the interference of light beams in between the multilayers. Multilayer-coated glass, however, has an intercepting effect which depends on the angle of incidence. More specifically multilayer-coated glass is capable of intercepting light beams of specific wavelength which are incident in a specific direction, but is incapable of shutting off light beams which are incident in other directions. In addition, multilayer-coated glass shows a gradual inclination in the graph under JIS B 7113 and can not give a high intercepting effect.